Contrary to what you’ll see in most action movies, bullets don’t actually travel through water very effectively at all. When a round impacts the water, it very literally impacts, often breaking apart or tumbling off of its trajectory because of the water’s density.
As we’ve covered here at SOFREP before, it doesn’t take much water to render most rounds inert — making it possible for Norwegian physicist Andreas Wahl to stand right in front of a submerged SIG SG 550 in a pool and use a rope to pull the trigger without fearing for his life.
For most folks, a weapon’s ability to take a life through the water isn’t a pressing concern; but for some very specific groups of war fighters, this presents a serious issue. Navy SEALs are known for conducting clandestine operations in and around the water, and Navy Frogmen are often tasked with preventing the foreign equivalent of our SEALs from doing the same near American shores. Because of this, specialized weapons have been developed over the years to allow them to do just that, like the Heckler & Koch P11 that saw heavy use during the Cold War — and likely still has a place in a few armories today.